Understanding Dutasteride and Finasteride
Dutasteride and finasteride are medications known as 5-alpha reductase inhibitors (5-ARIs) [1.2.1]. They are primarily used to treat benign prostatic hyperplasia (BPH), or an enlarged prostate [1.4.3]. Finasteride is also FDA-approved for treating androgenetic alopecia (male pattern hair loss), while dutasteride is often used off-label for the same purpose [1.2.2, 1.3.4].
Their main function is to block the 5-alpha reductase enzyme, which is responsible for converting testosterone into a more potent androgen called dihydrotestosterone (DHT) [1.4.2]. DHT is a key factor in both prostate growth and the miniaturization of hair follicles that leads to baldness [1.2.3].
The Difference in Mechanism
The 5-alpha reductase enzyme exists in two main forms: Type 1 and Type 2 [1.2.3].
- Finasteride selectively inhibits the Type 2 enzyme, which is predominant in hair follicles and the prostate. This action reduces serum DHT levels by approximately 70% [1.4.1, 1.4.2].
- Dutasteride is a dual inhibitor, blocking both Type 1 and Type 2 enzymes. This results in a more comprehensive suppression of DHT, reducing serum levels by 90% or more [1.4.1, 1.4.2].
Because of its broader action, studies have shown dutasteride to be more effective than finasteride at increasing hair count and thickness in clinical trials [1.3.3, 1.3.5, 1.4.6].
Can I Take Dutasteride and Finasteride Together?
Combining oral dutasteride and finasteride is generally not recommended by healthcare professionals [1.2.1, 1.2.4]. Since both drugs belong to the same class and target the same pathway, taking them together significantly increases the likelihood of adverse side effects without providing substantial additional benefits [1.5.1, 1.5.2]. The side effect profiles of both drugs are similar, and combining them amplifies the risk [1.5.2].
However, there are some nuances:
- Limited Studies: While most medical advice cautions against combination therapy, there is a lack of extensive research on the subject [1.2.5]. One small case study reported a dramatic increase in hair density when a patient on daily finasteride added a low weekly dose of dutasteride [1.3.2, 1.2.7]. Still, experts point out that switching to dutasteride alone might have produced the same result, as it is a more potent DHT blocker [1.2.5].
- Topical Formulations: Some dermatologists may prescribe a combination of topical finasteride and topical dutasteride. This approach aims to localize the DHT-blocking effect on the scalp, potentially reducing the risk of systemic side effects associated with oral medications [1.2.6, 1.5.2].
- Alternating Doses: There is no clinical evidence to support alternating days between finasteride and dutasteride as an effective hair loss management strategy [1.2.5]. Given the different half-lives of the drugs (finasteride's is much shorter than dutasteride's), a consistent daily regimen of one or the other is typically advised [1.2.2].
Risks and Side Effects of Combination
Combining two 5-ARIs is likely to increase the risk and potential severity of side effects common to both medications. These include [1.5.1, 1.5.2, 1.5.3]:
- Decreased libido (sex drive)
- Erectile dysfunction
- Ejaculation disorders (e.g., reduced volume)
- Gynecomastia (enlargement of male breast tissue)
- Dizziness
- Temporary hair shedding
Furthermore, the FDA has issued a safety communication noting that 5-ARIs may increase the risk of developing a more serious form of prostate cancer [1.6.1]. PSA levels should be monitored by a healthcare provider, as these drugs can lower them, potentially masking signs of prostate issues [1.6.7].
Comparison Table: Dutasteride vs. Finasteride
| Feature | Dutasteride (Avodart) | Finasteride (Propecia) |
|---|---|---|
| Mechanism | Inhibits Type 1 & Type 2 5-alpha reductase [1.4.2] | Inhibits Type 2 5-alpha reductase [1.4.2] |
| DHT Suppression | ~90% or more [1.4.1] | ~70% [1.4.1] |
| FDA Approval | BPH (off-label for hair loss) [1.3.4] | BPH and Male Pattern Hair Loss [1.3.4] |
| Standard Dose | 0.5 mg daily [1.2.6] | 1 mg daily (for hair loss) [1.3.4] |
| Efficacy | Studies show it is more effective for hair regrowth [1.3.5, 1.4.8] | Considered the gold standard and effective for most men [1.3.7] |
| Side Effects | Similar to finasteride, possibly slightly higher risk [1.4.2, 1.5.6] | Decreased libido, ED, ejaculation issues [1.5.8] |
Switching from Finasteride to Dutasteride
For individuals who are not achieving the desired results with finasteride, a more common and medically supported approach is to switch to dutasteride rather than combining the two [1.2.5]. This transition should always be done under the supervision of a healthcare provider [1.2.2, 1.2.6]. Your doctor can provide guidance on how to stop one and start the other, as finasteride leaves the body relatively quickly due to its shorter half-life [1.2.2].
Conclusion
While the idea of combining two powerful DHT blockers is appealing, current medical guidance advises against taking oral dutasteride and finasteride together. The potential for increased side effects generally outweighs the unproven benefits of combination therapy. Dutasteride is demonstrably more potent at suppressing DHT and has been shown in studies to be superior for hair growth compared to finasteride [1.3.5, 1.4.8].
If you are concerned about your progress on finasteride, the safest and most effective next step is to consult a hair loss specialist or dermatologist. They can assess your situation and determine if switching to dutasteride monotherapy or exploring other options, such as topical formulations or combination with minoxidil, is the right course of action for you [1.2.5, 1.6.3].
For more information on the class of drugs, you can review the FDA's page on 5-alpha reductase inhibitors.
